The present invention relates to the art of diagnostic imaging. It finds particular application in conjunction with nuclear or gamma cameras and will be described with particular reference thereto. It is to be appreciated, however, that the present invention will also find application in other non-invasive investigation techniques and imaging systems such as single photon planar imaging, whole body nuclear scans, positron emission tomography (PET), digital x-ray computed tomography and other diagnostic modes.
Single photon emission computed tomography (SPECT) has been used to study a radionuclide distribution in a subject. Typically, one or more radiopharmaceuticals or radioisotopes are injected into a patient subject. The radioisotope preferably travels to an organ of interest whose image is to be produced. The patient is placed in an examination region of the SPECT system surrounded by large area planar radiation detectors. Radiation emitted from the patient is detected by the radiation detectors. The detectors have a mechanical collimator to limit the detector to seeing radiation from a single selected trajectory or ray, often the ray normal to the detector plane.
Typically, the detector includes a scintillation crystal that is viewed by an array of photomultiplier tubes. The relative outputs of the photomultiplier tubes are processed and corrected, as is conventional in the art, to generate an output signal indicative of (1) a position coordinate on the detector head at which each radiation event is received, and (2) an energy of each event. The energy is used to differentiate between emission and transmission radiation and between multiple emission radiation sources and to eliminate stray and secondary emission radiation. A two-dimensional projection image representation is defined by the number of radiation events received at each coordinate.
In tomographic imaging, data collection is performed by either continuous rotation of the detectors or by "step-and-shoot" data acquisition where the detector is rotated at uniform intervals, typically 2 degree steps, over a 360 degree or 180 degree range. At each step position, radiation events or counts are acquired from a selected time interval. The data acquired from each step position (e.g. each projection view) are combined to reconstruct an image representation.
Positron emission tomography (PET) scanners are known as coincidence imaging devices. In planar coincidence imaging, two detectors oppose each other with a subject disposed between the detectors. The detectors view the subject along a longitudinal axis without rotation, otherwise known as limited angle tomography. Radiation events are detected on each detector and a coincidence circuitry compares and matches the events on each detector. Events on one detector which have a coincident event on the other detector are valid data and used in image reconstruction.
The above-mentioned acquisition protocols may not be optimal for a given imaging situation. Some angular detector positions offer more useful imaging information than other angles due to geometric effects, attenuation, scatter of radiation, and random coincidences. In a situation where the count rate is low, an optimal acquisition protocol will greatly improve image quality.
The present invention provides a new and improved data acquisition system and method for diagnostic imaging systems which overcomes the above-referenced problems and others.